Litecoin suffers 13-block reorg after MWEB vulnerability and DoS exploited — about 32 minutes of activity reversed
Litecoin experienced a 13-block chain reorganization late Friday into Saturday, rolling back roughly 32 minutes of network activity after attackers exploited a bug in the Mimblewimble Extension Block (MWEB) protocol. The incident allowed invalid MWEB peg-out transactions to be accepted by some miners, and a denial-of-service (DoS) component was used to influence which fork of the chain prevailed for a short period.
What happened
- Attackers leveraged a consensus-level MWEB bug that permitted invalid peg-out transactions to pass through nodes that had not yet upgraded. Those invalid transactions were included on a fork that ran for about 32 minutes before the network’s longest valid chain reasserted itself and rewrote 13 blocks.
- The Litecoin Foundation said the bug was fully patched and the network was operating normally by Asian morning hours on Sunday, and urged users to upgrade to Litecoin Core v0.21.5.4, which includes the fixes.
Timeline and patches
- According to public commit history and security researchers, the consensus vulnerability that enabled the invalid MWEB transactions was privately patched between March 19 and March 26 — roughly four weeks before the attack — but that patch was not public or widely enforced.
- A separate DoS vulnerability was patched the morning of April 25. Both fixes were rolled into release v0.21.5.4 later that same afternoon — after the attack had already begun.
- Because some miners were running the privately patched code while others ran unpatched versions, a split in the network created a window of vulnerability that the attackers appear to have exploited.
Evidence of premeditation
- Security researchers, including bbsz of the SEAL911 incident response group and Alex Shevchenko (CTO at NEAR Foundation’s Aurora project), have highlighted on-chain evidence suggesting the exploit was pre-funded and orchestrated. Blockchain data indicates the attacker funded a wallet 38 hours before the exploit via a Binance withdrawal, and the destination address was already set up to swap LTC into ETH on a decentralized exchange.
- Researchers contend the attack used two components in concert: the MWEB consensus bug to embed invalid transactions, and a DoS to take patched mining nodes offline so unpatched nodes would produce the fork containing those transactions. Once patched miners returned or the DoS subsided, the updated chain overtook the malicious fork and corrected the ledger.
Broader implications
- The incident underscores differences in how networks respond to urgent security fixes. Newer or more centralized chains can push coordinated upgrades quickly via validator communication channels. Older proof-of-work networks like Litecoin — where independent mining pools choose when to upgrade — can be slower to converge on emergency patches, creating exploitable windows.
- The Litecoin Foundation has not publicly addressed the discrepancy between the private patch timeline visible in the GitHub commit log and its public statements. The exact amount of LTC peg-outs included in the invalid blocks, and any value converted before the reorg reversed those transactions, has not been disclosed.
Current status
- The Foundation reported that patches have been applied and the network is operating normally. Users and miners are urged to upgrade to Litecoin Core v0.21.5.4 to ensure they are not running vulnerable code.
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